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TECHNICAL BRIEF

# Conditionally-Sampled Turbulent and Nonturbulent Measurements of Entropy Generation Rate in the Transition Region of Boundary Layers

[+] Author and Article Information
Edmond J. Walsh, Kevin P. Nolan

Stokes Research Institute, Department of Mechanical and Aeronautical Engineering, University of Limerick, Limerick, Ireland

Donald M. McEligot

Idaho National Laboratory (INL), Idaho Falls, ID 83415-3885

Ralph J. Volino

United States Naval Academy, Department of Mechanical Engineering, Annapolis, MD 21402

Department of Mechanical Engineering and Materials Science, Duke University, Durham, NC 27708-0300

J. Fluids Eng 129(5), 659-664 (Jan 08, 2007) (6 pages) doi:10.1115/1.2717622 History: Received September 30, 2005; Revised January 08, 2007

## Abstract

Conditionally-sampled boundary layer data for an accelerating transitional boundary layer have been analyzed to calculate the entropy generation rate in the transition region. By weighing the nondimensional dissipation coefficient for the laminar-conditioned-data and turbulent-conditioned-data with the intermittency factor $γ$ the average entropy generation rate in the transition region can be determined and hence be compared to the time averaged data and correlations for steady laminar and turbulent flows. It is demonstrated that this method provides, for the first time, an accurate and detailed picture of the entropy generation rate during transition. The data used in this paper have been taken from detailed boundary layer measurements available in the literature. This paper provides, using an intermittency weighted approach, a methodology for predicting entropy generation in a transitional boundary layer.

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## Figures

Figure 1

Conditionally-sampled velocity profiles and Reynolds shear stresses for stations 1–9: 엯, laminar-conditioned data; ▵, turbulent-conditioned data; ◆, turbulent-conditioned Reynolds shear stresses; ---, law of the wall, Y+=U+; —, Von Kármán empirical correlation U+=2.4lnY++5; —, sixth order polynomial fit of turbulent-conditioned Reynolds shear stress data

Figure 2

Entropy generation rate profiles for station 5: 엯, laminar-conditioned data; ▵, viscous turbulent conditioned data; —, Reynolds shear stress turbulent-conditioned data; ◻, total turbulent-conditioned data

Figure 3

Contours of nondimensional volumetric entropy generation rate for (a) laminar conditionally-sampled, (b) turbulent conditionally-sampled, (c) intermittency weighted data, and (d) nonconditionally sampled

Figure 4

Dissipation coefficient vs Reθ: ∎, laminar-conditioned data; ●, turbulent-conditioned data (note: station 1 data point for turbulent-conditioned data are located at Reθ=90); ▴, intermittency weighted data; ▵, unconditionally sampled data

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